1. Field of the Invention
This invention relates to building wall or roof structures and, more particularly, to composite metal panels with concealed fastening systems. The composite metal panel consists of a structural core material sandwiched between two exterior metal skins. The metal skins are commonly painted carbon steel, aluminum, or stainless steel of thicknesses ranging from 0.018" (0.46 mm) to 0.048" (1.22 mm). The skins act compositely to resist external bending loads such as wind or roof loads by way of shear transfer through the structural core. Structural foam, paper honeycomb, or aluminum honeycomb is normally utilized as the core material. The core is structurally connected to the metal skins by chemical or adhesive bond.
2. Description of the Prior Art
Composite metal panels have been widely used in building wall and roof structures due to their high strength-to-weight ratio. The depth of the panel normally ranges from 1 inch (25 mm) to 8 inches (203 mm), depending on load or thermal insulation requirements. The width of the panel normally ranges from 12 inches (305 mm) to 48 inches (1219 mm). The panels are fastened to the building frame members, such as horizontal wall girts, vertical mullions, or roof purlins in a side-by-side fashion to form the wall or the roof surface. The finished wall or roof surface must be sealed against air and water infiltration. The side joint between two panels is sealed by a proper sealant, such as caulking or gasket. To prevent relative movement between two panels at the side joint location from damaging the sealing property, the side joint is commonly profiled to have an engaging male and female joining device whereby the sealant is secured within the female groove. In order to conceal the fasteners, a fastener pocket is provided within the depth of the panel at the side joint locations. The erection procedure involves engaging one side of the panel (i.e., the free side) and fastening the other side to the building frame (i.e., the fixed side). The fastener head on the fixed side will be concealed by the exterior panel surface of the free side. Under negative wind load conditions (i.e., the internal pressure being greater than the external pressure), the free side tends to pull away from the fixed side. This tendency of side joint separation is resisted by the male and female joining device.
In addition to the structural and weather sealing requirements, a composite panel is often designed to provide thermal insulation. In this function, the exterior metal skin is arranged to have no contact with the interior metal skin to prevent through conductivity. Accordingly, one set of male and female joining devices is provided on each skin independently. On one side of the panel, there is an interior male spline and and exterior female groove while on the other side of the panel, there is an interior female groove and an exterior male spline. Normally, the exterior male spline is utilized to cover up the fastener pocket. Therefore, the side with the interior male spline is the fixed side of the panel.
As discussed above, the male and female joining device serves to provide a means for sealing the side joint and a structural component for resisting the side joint separation under load. The side joint strength is dependent on the bending stiffness of the male splines. Since the male spline is an extension of the metal skin which is a light gauge metal with limited stiffness, the panel strength is often governed by the side joint strength. It is also known that, to prevent premature skin delamination, it is necessary to allow the fastener on the fixed side to penetrate through both the exterior and the interior skins. The side joint strength limitation severely limits the use of lighter metal skin and/or wider panel.
There are two types of panel construction in wall application. The first type is to join the panels side-by-side to form vertical side joints which is referred to as vertical wall panel application. The second type is to join the panels side-by-side to form horizontal side joints which is referred to as horizontal wall panel application. The practical erecting procedure in the horizontal wall panel application is to erect the panel from the wall base working upwardly. In this manner, the side with the inerior male spline (i.e., the fixed side) must be positioned at the top before fastening. As a result, the exterior downward female groove is also positioned at the top side of each panel. In this configuration, any water infiltrated through the exterior seal will be trapped at the bottom of the exterior female groove creating the concern of steel skin rusting and side joint distortion due to freezing. To eliminate this problem, some existing commercial product manufacturers eliminate the engaging feature of the exterior skin. However, eliminating the exterior skin engagement further reduces the side joint strength and thus further reduces the span capability of the panel.
In recent years, it is an aesthetic preference to provide a wide exterior panel reveal joint at the side joint location whereby an accent color can be provided at the reveal joint. To provide the exterior reveal joint, the exterior male spline must be extended. As a result of extending the exterior male spline, the side joint strength is further reduced leading to a reduced span capability of the panel.